Inserting rotation keyframes
You can create cycles instantly using Curve modifiers, which are accessed through the Graph Editor window's Properties Shelf (press 'n' while mouse hovering over the Graph Editor Window to bring up the Shelf). Once the Properties Shelf is up, you will see tabs to the far right of it, one of which is Modifiers. Click on it.



In my example, I created two keyframes on the Global Z axis to make the cylinder rotate 360 degrees in 32 frames. Instead of making extra keyframes to add additional revolutions, I was able to create a cycle modifier, which automatically extends the rotations indefinitely. Setting the Repeat Motion: After field to 3 allows me to add three repeated revolutions to the original one, giving me four revolutions, total.

You may find, as I did, that something odd happens to the final keyframe in the original F-Curve after adding the Repeat Motion restriction, causing the cycled loops to have timing which does not connect seamlessly. I had to manually adjust the handles on the final keyframe for the original F-Curve after setting this up, for reasons unknown. Might be a bug. Just giving you a heads up.